This invention relates to railroad-crossing signal-gate mechanisms and, more particularly, to a motor controller for the use therein.
Railroad-crossing signal-gate mechanisms include a pivotally-supported gate arm which is movable between a horizontal signalling position and an upright storage or non-signalling position. The arm is mounted on a pivotable main support shaft which is driven by a motor that is controlled by a cam-type circuit controller associated with the shaft and responsive to the rotation of the shaft.
In order to raise the arm from the horizontal position to the upright position, the motor is energized and thereafter controlled and deenergized by a cam-assembly and an associated cam follower and switch assembly.
In existing circuit controllers, the cam assembly is mounted on the support shaft and engages the cam follower as the gate arm is raised so as to close the switch. When the gate arm reaches the upright position, the cam assembly and cam follower disengage, the switch opens and the arm-raising motor is deenergized. However, due to the slow rotation of the support shaft, the switch opens slowly and this has resulted in excessive arcing of the switch contact points.
It is therefore an object of this invention to provide a cam-type circuit controller in which the switch opens quickly so as to minimize arcing.
Furthermore, in existing gate control mechanisms it is possible that the gate arm may fail to lock in the upright position and thus oscillate (i.e., move back and forth) about the upright position. This is due to the gate arm swinging past the upright position, striking the gate arm stops, and bouncing back toward the horizontal position. On occasion the gate arm could bounce back sufficiently far that the cam assembly would reengage the cam follower, close the contact points, and thereby reactivate the raising motor. This process could continue indefinitely so that the arm-raising motor would be energized and deenergized on each oscillation. This has, in turn, resulted in occasional overheating and electrical failures within the mechanism.
It is therefore another object of this invention to provide an arm-raising motor controller which will minimize or eliminate arm oscillation.
These and other objects of this invention will become apparent from the following description and appended claims.